Late Pleistocene and Holocene Vegetation and Climate on the Taymyr Lowland, Northern Siberia
Andrei A. Andreev1and Christine Siegert
Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg A43, 14473 Potsdam, Germany
Vladimir A. Klimanov
Institute of Geography, Russian Academy of Sciences, Staromonetny 29, 109017 Moscow, Russia
Aleksandr Yu. Derevyagin and Galina N. Shilova
Geological Department of Moscow State University, Vorobievy Gory, 119899 Moscow, Russia
and Martin Melles
Institute for Geophysics and Geology, Leipzig University, Talstrasse 35, 04103 Leipzig, Germany Received February 6, 2001
Pollen records from perennially frozen sequences provide vege- tation and climate reconstruction for the last 48,00014C years in the central part of Taymyr Peninsula. Open larch forest withAlnus fruticosaandBetula nanagrew during the Kargin (Middle Weich- selian) Interstade, ca. 48,000–25,00014C yr B.P. The climate was generally warmer and wetter than today. Open steppe-like com- munities withArtemisia, Poaceae, Asteraceae, and herb tundra- like communities with dwarfBetulaandSalixdominated during the Sartan (Late Weichselian) Stade, ca. 24,000–10,30014C yr B.P.
The statistical information method used for climate reconstruction shows that the coldest climate was ca. 20,000–17,00014C yr B.P.
A warming (Allerød Interstade?) with mean July temperature ca.
1.5◦C warmer than today occurred ca. 12,00014C yr B.P. The fol- lowing cooling with temperatures about 3◦–4◦C cooler than present and precipitation about 100 mm lower corresponds well with the Younger Dryas Stade. Tundra–steppe vegetation changed toBetula nana–Alnus fruticosashrub tundra ca. 10,00014C yr B.P. Larch appeared in the area ca. 940014C yr B.P. and disappeared after 290014C yr B.P. Cooling events ca. 10,500, 9600, and 8200 14C yr B.P. characterized the first half of the Holocene. A significant warming occurred ca. 850014C yr B.P., but the Holocene tempera- ture maximum was at about 6000–450014C yr B.P. The vegetation cover approximated modern conditions ca. 280014C yr B.P. Late Holocene warming events occurred at ca. 3500, 2000, and 100014C yr B.P. A cooling (Little Ice Age?) took place between 500 and 200
14C yr ago. °C2002 University of Washington.
1To whom correspondence should be addressed. E-mail: aandreev@awi- potsdam.de.
Key Words: pollen; vegetation and climate reconstruction; Late Pleistocene; Holocene, Arctic Russia; Taymyr Peninsula.
INTRODUCTION
The Arctic is highly sensitive to climate variations and is con- sequently an important region for understanding present and past climate changes. The Taymyr Peninsula, situated in a transition zone between marine-influenced West Siberia and the more con- tinental East Siberia, is a region which is particularly sensitive to climate fluctuations. The Late Pleistocene environment of the Taymyr has been the subject of continuous debate, mostly due to a lack of empirical data. Theoretically based hypotheses pro- pose that a huge Arctic Ice Sheet covered the area during the Late Pleistocene (Grosswald, 1998). However, field data indi- cate that the glaciation was restricted to mountain areas (Isaeva, 1984; Faustova and Velichko, 1992).
To improve our knowledge about the Late Quaternary of Central Siberia, a multidisciplinary German–Russian research project, “Taymyr,” was established in 1993. Within the scope of the project, palynological studies were carried out at a number of sites along a transect from the vicinity of Norilsk in the south to the Taymyr Lake in the north (Hahne and Melles, 1997, 1999;
Kienel et al., 1999; Siegert et al., 1999). The transect covers veg- etation zones from the arctic tundra to the northern taiga (Fig. 1).
In this paper we present the vegetation and climate history for the Labaz Lake area (Fig. 1) during the last 48,000 yr based on 10 pollen profiles.
0033-5894/02 $35.00 138
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FIG. 1. (A) Map of the Arctic. (B) Map of Taymyr-Severnaya Zemlya region. (C) Overview map of Labaz Lake area with investigated sites.
STUDY AREA
Labaz Lake (72◦N, 99◦E) is one of the largest lakes in the North Siberian Lowland (Fig. 1). The modern lake can be re- garded as a relic of a huge ice-dammed “pre-Labaz Lake”
(Siegert et al., 1999). The geological and cryolithological struc- tures of the sediments reflect no glaciation after the Zyryan (Early Weichselian) Glaciation. Late Pleistocene landscape changes were connected with the decay of Zyryan-age glaciers.
FIG. 2. Generalized section of Late Quaternary sediments in the northern shore of Labaz Lake.
Changes in the size and level of the pre-Labaz Lake, thermoero- sion, and thermokarst processes formed the modern Labaz Lake, a number of smaller lakes, and terraces in the area. Late Pleis- tocene and Holocene sediments include lacustrian and fluvio- lacustrian sands, silts, clay, and peat deposits (Siegert et al., 1999).
Climate is characterized by long (8-month), severe winters and short, cold summers. The modern climate characteristics for the area are ca. 10◦to 12◦C for July temperatures,−32◦ to
−34◦C for January temperatures,−12◦ to−14◦C for annual mean temperature, and about 300 mm for annual precipitation (Atlas Arktiki, 1985). The frost-free period is ca. 70–75 days per year.
Soils in the area are mainly gleyed cryosols with an active layer of ca. 30–40 cm. Thickness of the permafrost is 300–
600 m. Labaz Lake is situated near the boundary of the southern and typical tundra zones. Shrubs, including Betula exilis and Salix ssp. dominate the vegetation. Dwarf shrub species include Vaccinium vitis-idea, Empetrum hermaphroditum, and Dryas punctata. Carex ssp., Eriophorum vaginatum, and mosses such
TABLE 1
Radiocarbon Dates from the Labaz Lake Area Sequences
Site name, Age δ13C
depth (cm) Dated material (14C yr B.P.) (‰PDB) Laboratory # Method 1 LAO22, 250–270 Indeterminate woody remains >48,000 −28.2 LZ-1271 LSC
2 LAO22, 570–610 Indeterminate woody remains >46,000 −29.3 LZ-1272 LSC
3 LAO22, 640 Indeterminate woody remains >44,500 −29.6 LZ-1273 LSC
4 LAO22, 680–720 Indeterminate woody remains >48,000 −28.5 LZ-1274 LSC
5 LAO1, 45–85 Peat >40,000 −29.0 AWI-84 LSC
6 LAO1, 85–120 Peat >40,000 −27.4 AWI-82 LSC
7 LAO1, 120–145 Indeterminate shrub twigs >40,000 −28.7 AWI-83 LSC 8 LAO1, 120–145 Indeterminate woody remains >48,000 −29.0 LZ-1275 LSC
9 LAO25, 280 Woody peat 28,500±400 −28.1 AWI-96 LSC
10 LAO25, 350 Woody peat 38,000±600 −27.2 AWI-97 LSC
11 LAO25, 350 Indeterminate shrub twigs >40,000 −29.4 AWI-122 LSC
12 LAO25, 430 Indeterminate tree twigs 33,600±400 −28.1 AWI-103 LSC
13 LAO25, 430 Indeterminate tree twigs 38,900±1300 −27.8 AWI-123 LSC
14 LAO25, 510 Indeterminate shrub twigs >40,000 −28.8 AWI-121 LSC
15 LAO28, 150 Indeterminate plant remains 17,320±220 −27.7 KIA1413 AMS 16 LAO28, 160 Indeterminate plant remains 16,710±60 −28.67 KIA5753 AMS
17 LAO6, 60–65 Peat 7860±90 −23.5 LZ-P5 LSC
18 LAO6, 110–120 Peat 8760±90 −31.1 LZ-P6 LSC
19 LAO6, 200 Indeterminate plant remains 26,240+580/−540 −26.5 KIA1414 AMS 20 LAO6, 240 Indeterminate plant remains 14,390+150/−140 −27.7 KIA1415 AMS 21 LAO6, 340–360 Indeterminate plant remains 34,500±900 −30.5 LZ-1269 LSC 22 LAO6, 660–680 Indeterminate plant remains 38,000±1600 −33.2 LZ-1270 LSC 23 LAO6, 660–680 Indeterminate plant remains 29,000±320 −30.0 AWI-120 LSC
24 LAB2-94, 40 Peaty soil 2900±50 −28.4 AWI-105 LSC
25 LAB2-94, 36–40 Peaty soil 4200±60 −29.4 LZ-1278 LSC
26 LAB2-94, 50–57 Indeterminate plants remains 5770±70 −28.16 KIA1406 AMS 27 LAB2-94, 140–150 Indeterminate plant remains 6580±70 −28.11 KIA1407 AMS 28 LAB2-94, 225–240 Indeterminate plant remains 7360±60 −25.1 KIA1408 AMS 29 LAB2-94, 295–305 Indeterminate plant remains 8960±90 −27.9 KIA1409 AMS 30 LAB2-94, 324–332 Indeterminate plant remains 8710±100 −28.39 KIA1410 AMS 31 LAB2-94, 365–375 Indeterminate plant remains 20,400+300/−290 −29.8 KIA1411 AMS 32 LAB2-94, 379–385 Indeterminate plant remains 24,990+520/−480 −26.6 KIA1412 AMS
33 LAB12-95, 98–102 Peaty soil 4700±70 −28.9 LZ-1280 LSC
34 LAO13-94, 10 Peaty soil 920±60 −26.6 LZ-P9 LSC
35 LAO13-94, 70–80 Peat 9280±100 −26.8 LZ-P10 LSC
36 LAO13-94, 135 Indeterminate plant remains 11,810±140 −28.0 KIA1416 AMS
37 LAO14, 40–45 Peaty soil 6730±80 −28.9 LZ-P11 LSC
38 LAB2-95, 92–104 Peat 9150±130 −27.7 LZ-1279 LSC
39 LAB2-95, 92–104 Indeterminate twigs 8850±115 −29.1 LZ-1276 LSC
40 LAB3-95, 30–60 Peat 2230±60 −27.9 LZ-1277 LSC
LZ—University Leipzig; AWI—Alfred Wegener Institute, Potsdam; KIA—Leibniz Laboratory, Kiel; LSC—ages obtained by liquid scintillation counting method; AMS—accelerator mass spectrometry.
as Tomenthypnum nitens and Drepanocladus uncinatus charac- terize wetter sites. Alnus fruticosa grow on south-facing slopes.
Occasional specimens of Larix dahurica krummholtz were also found near the lake.
METHODS
Perennially frozen sequences of fluvio-lacustrian sands, silts, clay, and peat sediments were collected from five exposures and five bore holes (Figs. 1 and 2). Sediments were measured, cleaned to expose frozen deposits, and cut for transport into
TABLE 2
Radiocarbon-Dated Wood Remains from the Labaz Lake Area
Age δ13C,
# Site name and description Dated material (14C yr B.P.) (‰ PDB) Laboratory #
1 LAO27, steep slope of the Kokora Lake terrace, 400 cm above the lake Indeterminate wood remains 8390±70 −26.7 AWI-104 2 Near the LAB2-95, on a shore of small thermokarst lake Larix stump 7790±60 −27.3 AWI-93
3 LAO17, 1050 cm above the Labaz Lake, under peat bed Larix trunk 7230±90 −26.7 LZ-P15
4 LAO26, steep slope of the Kokora Lake terrace, 650 cm above the lake Larix trunk 7170±100 −26.0 AWI-102 5 LAB1-94, a first terrace of the Tolton-Pastakh-Yuryakh River, under peat
bed, on the 260-cm depth
Larix trunk 7010±80 −26.4 LZ-P21
6 LAO31, first terrace of the Tolton-Pastakh-Yuryakh River on the 150-cm depth
Larix wood 6360±80 −28.0 AWI-87
8 LAO18, Labaz Lake terrace, on the 100-cm depth Indeterminate wood remains 6120±80 −27.3 AWI-91 9 LAO30, first terrace of the Tolton-Pastakh-Yuryakh River, on the
250-cm depth
Indeterminate wood remains 5780±60 −27.2 AWI-101 10 LAO15, Labaz Lake terrace, on the 80-cm depth Indeterminate wood remains 5710±100 −26.5 AWI-89 11 LAO15, Labaz Lake terrace, on the 80-cm depth Indeterminate wood remains 5410±50 −26.5 AWI-94 12 Near the LAO3, on the shore of a small thermokarst lake Larix trunk 5220±80 −25.9 LZ-P3 13 In situ in the soil (first terrace of the Tolton-Pastakh-Yuryakh River) Larix stump 4780±80 −26.0 LZ-P2 14 LAO29, thermokarst depression on the buried on the 50 cm depth Indeterminate wood remains 3700±70 −27.5 AWI-88
15 Near the LAO24, in a small thermokarst depression Larix stump 3680±70 −26.0 AWI-92
16 Near the LAB13-95, in situ, in a small thermokarst depression Larix stump 2880±60 −27.6 AWI-90 LZ-University Leipzig; AWI-Alfred Wegener Institute, Potsdam.
sample bags. Materials for14C dating were collected separately.
A total of 175 samples were analyzed for palynomorphs and 40 samples were radiocarbon dated (Table 1). Woody remains from the sections and from the modern surface were also col- lected and14C dated as well (Table 2).
A heavy-liquid separation method (Berglund and Ralska- Jasiewiczowa, 1986) followed by acetolysis and glycerin mounts was used in Moscow to process samples from nine sections.
Samples from the 10th section were processed in G¨ottingen by a chemical digestion method (Kienel et al., 1999). Pollen percentages were calculated based on the total pollen sum, and percentage of spores was based on a sum of pollen and spores. Pollen zonation was done by visual inspection. The TILIAGRAPH program was used for graphing the pollen data.
The statistical information method has been used to recon- struct climatic changes from fossil pollen spectra (Klimanov, 1976, 1984). This method is based on the statistical correlations between the total pollen and spore abundance, as well as that of tree and shrub pollen in the surface pollen spectra with modern climate conditions around the sampling sites. More than 800 recent pollen spectra from 220 sites across the former USSR were used to work out the technique (Klimanov, 1976). Modern climate variables are taken from the Klimaticheskiy Atlas SSSR (1960). Climatic variables used in the reconstructions comprise mean annual (Tyr), January (TI), and July (TVII) temperatures and total annual precipitation.
Treatment of these data by information analyses resulted in the preparation of tables that revealed the correlation of recent pollen data and the four climatic variables (Klimanov, 1976,
1984). Normalized coefficient of contingency for the data (value of correlation between the pollen types and the climatic vari- ables) shows that arboreal pollen taxa provide the best estimate of each climatic characteristic. The statistical relationship ex- isting between recent spectra and present climate conditions can be used to reconstruct past climate. The most probable value of the paleoclimatic variable for a particular pollen spec- trum corresponds to the largest sum of the classification crite- rion obtained from all the pollen in the spectrum (Klimanov, 1984).
The reliability and accuracy of the prepared tables for recon- structing climatic variables were determined by reconstructing present-day mean climate characteristics from modern spectra.
The main statistical errors for the reconstructions were±0.6◦C for Tyrand TVII,±1.0◦C for TI, and±25 mm for precipitation (Klimanov, 1976, 1984). As the method is based mostly on the statistical correlations between the arboreal pollen and modern climate conditions, it works more reliably for the Holocene, in which arboreal pollen dominate in pollen spectra, than for the Late Pleistocene, in which nonarboreal pollen dominated in the spectra.
Conventional14C dates on bulk sediments and accelerator mass spectrometry 14C dates of terrestrial macrofossils (Table 1) provided chronological control for the investigated sites. Pollen stratigraphy from the well-dated sites was also used for chronological control of the poorly dated sequences. Because we cannot provide good radiocarbon chronological control for all sequences, especially for those of the Late Pleistocene, ages of the reconstructed environmental events are uncalibrated.
RESULTS AND DISCUSSION
Ages of the studied sequences span from>48,00014C yr B.P.
to the present. As detailed descriptions of the sites are already published (Siegert et al., 1995, 1996, 1999; Kienel et al., 1999), we will not describe them in this paper but will describe changes in pollen assemblages and possible environmental meanings of these changes.
Kargin (Middle Weichselian) Interstadial
Generally, the Kargin (Middle Weichselian) sediments are widely distributed in the North Siberian Lowland; they form the lake terraces around the Labaz Lake (Fig. 2). The two best dated sections; LAO22 and LAO25, were studied for pollen and spores.
The wood remains from the LAO22 section (Fig. 3) have infinite radiocarbon dates from>48,000 to>44,50014C yr B.P. Similar dates were also obtained from the LAO1 site (Table 1). Betula nana and Alnus fruticosa pollen dominate the pollen spectra in both sites. Rare Larix pollen occurs in the spectra as well.
Similar pollen spectra from the adjacent areas are dated from 46,600±1200 to 42,600±150014C yr B.P. (Andreeva, 1982).
Such spectra are almost identical to the surface spectra from
FIG. 3. Percentage pollen and spore diagram of the LAO22 site (72◦220600N, 99◦420200E). 1—sand, 2—silty clay.
northern limit of larch taiga in the Taymyr Peninsula (Clayden et al., 1996) and reflect similar vegetation.
Although Larix is an important species of the forests in north- ern Eurasia, its history is not well known because of its poor pollen preservation. Larix pollen are rare even in surface samples from larch forests, and their low pollen frequency does not re- flect the actual abundance of Larix in the forest (e.g., Vas’kovsky, 1957; Popova, 1961; Clayden et al., 1996). Thus, even rare Larix grains in pollen records are interpreted as the presence of Larix in the local vegetation.
Alnus fruticosa, Betula nana, and Larix grew near Labaz Lake prior to 48,00014C yr B.P. Low concentrations of other tree pollen may reflect long-distance wind transport. However, high concentrations of redeposited Tertiary pollen show that these latter pollen grains were most likely also reworked from older sediments. Lycopodium spores are abundant in the section. They also may be reworked, as Lycopodium spores are more resistant to destruction. Alternatively, Lycopodium also may have grown in the area, as high amounts of Lycopodium spores are char- acteristic of Holocene sediments from Lama Lake (Hahne and Melles, 1997) and further suggest a northern taiga vegetation around the Labaz Lake area ca. 48,00014C yr B.P.
FIG. 4. Percentage pollen and spore diagram of the LAO25 site (72◦220700N, 99◦440500E). 1—clayey sand, 2—sand with peat layers, 3—sand.
Climate reconstructions show that Tyr, TI, and TVII could be 2.5◦–3◦C and precipitation 75–100 mm higher than today.
The actual age of this warming cannot be dated by the ra- diocarbon method. We suggest it may correspond to the Early Kargin (Early Middle Weichselian) period, ca. 50,000–
44,000 yr14C B.P. (Isaeva, 1984). Geological evidence confirms this age (Siegert et al., 1996).
Shrub remains from the bottom of the LAO25 section (Fig. 4) were radiocarbon dated to>40,00014C yr B.P. The pollen spec- tra from zone I (LAO25) are similar to all spectra from the LAO22 section (Fig. 3) and reflect the similar vegetation. The low content of Alnus fruticosa pollen may reflect deteriorating climate. Climate reconstructions indicate that the climate condi- tions could be slightly warmer and wetter than today, with Tyr, TI, and TVIIca. 0.5◦C and precipitation 25 mm higher than to- day. The bottom samples in the LAO25 section also indicate the Kargin age, but they could be younger than sediments from LAO22 and might be deposited at the beginning of the middle Kargin warm interval, ca. 44,000–42,00014C yr B.P. (Isaeva, 1984).
The remains of tree branches from a depth of 430 cm (LAO25) were radiocarbon dated to 38,900±1300 and 33,600±40014C yr B.P. We believe that the younger date is more reliable. The older date probably reflects the reworked character of all macro- fossils in the section due to the fluvio-lacustrine (or deltaic) origin of the sediments (Siegert et al., 1999). We assume the pollen spectra from zone II (LAO25) to have an age not older than 33,60014C yr B.P. Open Larix forests with Alnus fruticosa and Betula nana dominated the area at that time. Tyr, TI, and TVIImight be ca. 1.5◦C and precipitation 50–75 mm higher than today.
An increase of Betula nana in the upper part of zone II (LAO25) and decrease in Alnus fruticosa percentages indicates vegetation changes. This may indicate that a relative deteri- oration of climate occurred ca. 32,000 14C yr B.P., accord- ing to interpolation from the radiocarbon date: 33,600± 40014C yr B.P. from the 430-cm depth. This is in good agree- ment with a cooling on the Taymyr Peninsula at ca. 33,000–
30,00014C yr B.P. that was previously noted in radiocarbon- dated pollen records (Isaeva, 1984). Temperatures might be
1◦–1.5◦C and precipitation about 25 mm higher than modern values.
Woody remains from the 350-cm depth (LAO25, bottom of zone III) were14C dated to 38,000±600 and>40,000 yr B.P.
Because these dates seem to be too old compared with the other dates, suggesting that these macrofossils are reworked, we re- jected them. The amount of Alnus fruticosa pollen reaches maxi- mum values, whereas Betula nana percentages are at a minimum in zone III. Such spectra are typical of modern Larix taiga with Alnus fruticosa. All temperatures might be about 2◦C and pre- cipitation about 100 mm higher than today. An amelioration of climate may correspond with the beginning of a Late Kargin warming about 30,00014C yr B.P. (Isaeva, 1984). This is well correlated with data from the northern-situated Cape Sabler site, where some boreal plant remains were found in the sample radio- carbon dated to 29,970±79014C yr B.P. (Kienast et al., 2001).
Betula nana pollen dominate zone IV (LAO25), probably reflecting significant vegetation and climate changes. Shrubby tundra was dominant. Climate was probably similar to that of the present. This relatively cold event may have occurred ca.
28,600–28,80014C yr B.P., according to the 28,500±40014C yr B.P. date from the 280-cm depth.
Pollen spectra from zone V (LAO25) indicate that the vegeta- tion was similar to the modern Larix taiga near its northern limit.
FIG. 5. Percentage pollen and spore diagram of the LAB2-94 site (72◦2301800N, 99◦4101500E). 1—peaty soil, 2—peat, 3—loess-like loam, 4—silt with detritus, 5—sand.
During this late Kargin warming temperatures might be about 1◦C and precipitation about 50 mm higher than today. This is correlated well with data from the Cape Sabler, where macrofos- sils of boreal elements (e.g., Populus) were found in the sample radiocarbon dated to 26,750±65014C yr B.P. (Kienast et al., 2001). Kienast estimates that TVIIcould be up to 6◦C higher than today in the Cape Sabler area.
Because recent cryogenic and soil processes influenced the uppermost part of the LAO25 section it was not studied. Al- though, Late Kargin sediments from the areas adjacent to Labaz Lake were radiocarbon dated from 30,000 to about 24,00014C yr B.P. (Andreeva and Kind, 1982, Isaeva, 1984), we have no available records for the Late Kargin/Sartan transition.
Sartan (Late Weichselian)
The Sartan sediments were found in bore holes and sec- tions on the northern shore of Labaz Lake (LAO6, LAB2-94, LAB2-95, LAB12-95, LAB13-95), around Kokora Lake (LAO28), and on the southern shore of Labaz Lake (LAO13 and LAO14) (see Fig. 1). Unfortunately, we do not have good age control for this interval. The most detailed section is LAO6 (Fig. 5), which consists of about 5 m of silty clay sediments (Siegert et al., 1999). Plant macrofossils from the bottom were
14C dated to 38,000±1600 and 29,000±32014C yr B.P. Both
dates are too old considering the pollen spectra of the sediments, which contain large amounts of herb pollen including Artemisia, Poaceae, Caryophyllaceae, and Asteraceae. Relatively high con- tent of Larix pollen is noticeable in the lower part of the LAO6 section, especially at the bottom. This may partly reflect the reworked character of the organic matter in the Sartan sedi- ments, confirmed by radiocarbon dating. However, if this was the case, we should have large amounts of Alnus pollen as well.
A more likely explanation of the high content of Larix pollen is the existence of a local Larix refuge near the site during the early Sartan. The spectra are very different from those of Kar- gin, but almost identical to the pollen spectra of Late Glacial deposits from Lama and Levinson-Lessing Lakes (Hahne and Melles, 1997, 1999). Similar character of pollen spectra from the bottom of the LAB2-94 (Fig. 6) and LAO132sections and from the dated samples of LAO28 site (Table 1), which are radiocarbon dated to the Sartan interval, also confirm the Sar- tan age of the bottom sediments of LAO6. Generally, Sartan lacustrine and alluvial deposits are widespread in the Eastern Taymyr lowland. Radiocarbon dates obtained from such sedi- ments range from 21,400±1000 to 11,600±20014C yr B.P.
(Isaeva, 1984).
The other radiocarbon dates obtained from the Sartan part of LAO6 (34,500±900,26,240±580, and 14,390±15014C yr B.P.) are also not in a chronological order, reflecting the re- worked character of the dated material. We believe that the ear- liest date is the most reliable, as there is no evidence of possible contamination of the sediments by earlier organic material, so we assume that the pollen spectra from zone I (LAO6) were deposited during the Sartan.
The plant remains from the bottom part of the LAB2-94 section (zone I, Fig. 6) also show surprisingly old ages, con- trasting with the Holocene dates of the overlying sediments.
Although the oldest date is from the Late Kargin, the pollen spectra are typical (dominance of Artemisia and Poaceae) for Sartan. Most likely the dated plant remains were reworked from older sediments.
Low pollen concentration and large amounts of reworked Tertiary pollen are typical for Sartan deposits on Taymyr Peninsula (Hahne and Melles, 1997, 1999; Siegert et al., 1999).
Numerous unvegetated areas, caused by cryogenic processes, could be possible sources for reworked material. Pollen of plants typical of disturbed soils (e.g., Chenopodiaceae and Asteraceae) are also common in the spectra. The vegetation was probably very discontinuous during the Sartan. Another possible explana- tion of low pollen concentration might be low pollen productivity of plants due to extreme climate conditions.
The pollen data suggest that open steppe-like plant com- munities with Artemisia, Poaceae, Asteraceae, and Caryophy- llaceae dominated the vegetation around the pre-Labaz Lake.
2We cannot publish diagrams of all investigated sites in this paper, but detailed diagrams of all sites are available via Word Date Center—A for Paleoclimatology (http://www.ngdc.noaa.gov/paleo/pollen.html).
Tundra-like communities with Betula nana, arctic Salix, Dryas, Saxifraga, Oxyria, Carex, and some Brassicaceae (such as Draba) were common in more mesic sites. Rare pollen of trees and other shrubs are most likely reworked from older sediments.
Because of poor dating control and large amounts of reworked pollen, it was difficult to make reliable climate reconstructions for the Sartan interval. However, the data from the LAO6 site indicate that the coldest climate occurred ca. 20,000–17,00014C yr B.P. Temperatures could be 4◦–5◦C and precipitation about 75–100 mm lower than modern values. Similar characteristics were obtained from the LAO28 site spectra dated to 17,320± 220 and 16,710±60 14C yr B.P.; which were 3◦–4◦C below modern values for TVII, 5◦–5.5◦C for TI, and 4◦–4.5◦C for Tyr; precipitation was 50–75 mm lower than modern values.
The late Sartan records are preserved in several sites: LAO6 (Fig. 5), LAO13, LAB13-95, LAO14, LAB12-95, and LAB2- 95. Unfortunately, only two14C dates, 14,390±150 (LAO6) and 11,810±14014C yr B.P. (LAO13), were obtained from the Sartan part of these sections. Peaks of Betula nana in zone II of LAO6 (Fig. 6) and zone I of LAB12-95, may reflect a warming corresponding to the Allerød. The Arctic Ocean coastline was further to the north compared to today, which contributed to a more continental climate: TVIIcould have been 1.5◦C warmer than today, TIwas 1◦C lower, and Tyrwas close to the modern values. Precipitation was about 25 mm higher than today. As the method of climate reconstruction is based mostly on the statisti- cal correlations between the modern arboreal pollen and modern climate, the Late Glacial and Holocene climate reconstructions are more reliable than those from the Kargin and especially from the Sartan records. The averaged climate reconstructions for the last 12,00014C yr B.P. are presented in Figure 7.
A decrease of Betula nana pollen percentages and an increase of herb taxa in the upper part of the zone II of LAO6 (Fig. 5) may correspond to the Younger Dryas cooling. Peaks of Artemisia pollen in zone I of LAB13-95 diagram and zone II of LAB12-95 diagram also reflect the deterioration of climate at the late Sartan.
Similar herb-dominated pollen spectra from the Kheta River val- ley were dated to 10,860±15014C yr B.P. (Nikol’skaya et al., 1980). Temperatures might be about 3◦–4◦C and precipitation about 100 mm lower than modern values (Fig. 7).
Holocene
The Pleistocene–Holocene transition in the LAO6 (Fig. 5), LAB2-94 (Fig. 6), LAO13, LAB13-95, LAO14, LAB12-95, and LAB2-95 diagrams is characterized by dramatic decreases of herb pollen percentages, especially steppe and tundra taxa (e.g., Artemisia, Dryas, Poaceae, Caryophyllaceae, Asteraceae, Sax- ifraga). In contrast, significant increase of Betula nana, Alnus fruticosa, and Ericales percentages are noticeable in most dia- grams. We do not have radiocarbon dates of this transition, but we assume this interval is ca. 10,300–10,00014C yr B.P., similar to other regions of northern Eurasia (Klimanov, 1996; Velichko et al., 1997; Andreev et al., 1997).
FIG.6.PercentagepollenandsporediagramoftheLAO6site(72◦2301800N,99◦4203000E).1—peat,2—clayeysand,3—soil,4—siltyclay.
FIG. 7. Averaged paleoclimate curves from Labaz Lake sites pollen.
Sartan tundra–steppe vegetation was replaced by Betula nana–Alnus fruticosa shrub tundra ca. 10,00014C yr B.P. Peaks in Alnus fruticosa pollen percentages appear at different times in the early Holocene pollen records, probably reflecting varying environmental conditions around these sites and/or variation in local pollen depositional characteristics. In the beginning of the Holocene, Alnus fruticosa probably grew only in well-protected places similar to the present situation. The early Preboreal pe- riod, at ca. 10,000–980014C yr B.P. was characterized by temper- atures of about 1.5◦C and precipitation 50 mm higher than today.
At ca. 9600–930014C yr B.P., temperatures were about 2◦C and precipitation about 25 mm below modern values (Fig. 7).
Most likely Larix forest established in the Labaz Lake area at the end of the Preboreal period, at ca. 9200–900014C yr B.P. The oldest wood remains found in situ in the area were radiocarbon dated to 8390±7014C yr B.P. (Table 2). However, radiocar- bon dates from levels containing Larix pollen in the LAO13 and LAB2-95 sections suggest Larix may have been present as early as 9400–920014C yr B.P. Dates of 9200±40,9180±100, and 9000±15014C yr B.P. were obtained from sediments contain-
ing pollen and wood of Larix in adjacent areas (Nikol’skaya et al., 1980; Nikol’skaya, 1982). Similar data are known from West Taymyr (Clayden et al., 1997) and West Siberia (Peteet et al., 1998). Probably, Larix and Alnus fruticosa grew only in more protected places by the early Holocene, whereas Betula nana–Salix shrub tundra communities dominated the Labaz Lake area. At the end of Preboreal period (9200–900014C yr B.P.) TVIIwas about 1◦C, TIand Tyrabout 1.5◦C, and precip- itation was about 25 mm higher than today (Fig. 7).
Increases of Larix and tree Betula pollen content are no- ticeable in zone III (LAO6) and zone II (LAB2-94) and dated to the middle Boreal period, ca. 8800–8700 14C yr B.P. The wood remains (indeterminate pieces of wood, tree Betula bark, Larix cones) from the Kokora Lake vicinity (LAO27) were dated to 8390±70 14C yr B.P. A similar increase in Larix pollen percentages occurred in a peat dated to 8600±7014C yr B.P. from the Boganida River valley, ca. 50–100 km south of our sites (Nikol’skaya et al., 1980). The 14C-dated Larix and Betula remains from the currently treeless tundra on the Taymyr Peninsula show similar ages (Nikol’skaya, 1982;
MacDonald et al., 2000). Thus, Larix forests with tree Betula were widespread in the area ca. 8600–840014C yr ago. At that time, the so-called Boreal thermal optimum, temperatures were 2◦–3◦C warmer and precipitation 75–100 mm higher than those of today (Fig. 7). Similar characteristics were obtained by an analog method based on macrofossil data (Koshkarova, 1995).
According to these reconstructions TIwas 4◦–6◦C, TVII2◦C, and summer precipitation about 80 mm higher than those at present.
A decrease of tree and shrub pollen percentages in the zone III (LAB2-94), Figure 6, may correspond with a cooling at about 820014C yr B.P. noted in the Northern Eurasia (Klimanov, 1996).
Temperatures were about 1◦C and precipitation about 25 mm below modern values (Fig. 7).
Shrubs and tree pollen percentages increase again in the sed- iments dated at about 800014C yr B.P. (the upper part of the zone III of LAO6, Fig. 5; the bottom part of the zone IV of LAB2-94, Fig. 6), reflecting changes in the vegetation. Most of the dated Larix remains from the area belong to the Atlantic pe- riod (Table 2). Tree Betula macrofossils from the Kokora Lake vicinity were dated to 5180±18014C yr B.P. (Kul’tina et al., 1974). Similar dates of Larix wood were also obtained from adjacent areas (Kremenetski et al., 1998; MacDonald et al., 2000). Minor amounts of Larix and Betula sect. Albae pollen and abundant Alnus fruticosa pollen are also found in spectra from adjacent regions. These assemblages have also been14C dated to the Atlantic period (Kul’tina et al., 1974; Belorusova and Ukraintseva, 1980; Nikol’skaya et al., 1980; Belorusova et al., 1987). The data show that Larix forest with tree Betula grew in areas that today are dominated by shrub tundra. Al- nus fruticosa and dwarf Betula shrub communities were also common. The warmest period during the Holocene occurred ca.
6000–450014C yr B.P., with maximum temperatures 2.5◦–3◦C and precipitation 100 mm higher than today at about 550014C yr B.P. (Fig. 7).
Climate characteristics obtained by Koshkarova (1995) on the Taymyr Peninsula for the first half of the Atlantic period (8000–6500 14C yr B.P.) are similar to ours. TI is about 1◦C higher than at present according to Koshkarova’s and 1◦–2◦C by our method, and TVIIis 2◦C and 1◦–1.7◦C higher than at present. Reconstructed precipitation shows a larger difference:
130–180 mm higher than at present according to Koshkarova and only 25–50 mm by our method. Climatic characteristics for the second half of the Atlantic period (6000–450014C yr B.P.) show similar differences: TIis about 5◦C and 2◦–3◦C, and TVIIis 2◦C and 1◦–2.5◦C higher than at present. Precipitation, reconstructed by Koshkarova, is 50 mm lower then at present during the winter and 120 mm higher during summer. Mean annual precipitation, reconstructed by our approach, is 60–100 mm higher than at present.
The comparison of the climate parameters reconstructed by these different methods shows that TVIIare very close to each other, whereas the difference in TIis greater than that in TVII. The information statistical method has a better correlation between the modern TVIIand modern pollen taxa than between TI and
those. This is probably because all plants experience summer temperature, but most plants are protected from winter frost by snow. It is unclear why precipitation reconstructed by the two methods are rather close in the Boreal period and so different dur- ing the first half of the Atlantic period. One possible explanation is that the peat exposures, investigated by Koshkarova, are situ- ated in the area where precipitation is rather high (up to 800 mm) at the present, compared with 300 mm near Labaz Lake. This difference was probably even higher during the Atlantic period.
An increase in Ericales pollen percentages in zone IV (LAB 12-95) and an increase in herbs at the bottom of zone II (LAB3- 95) suggests a significant cooling. This event may be correlated with the cooling at about 450014C yr B.P., recorded in many sites from northern Eurasia (Klimanov, 1996; Velichko et al., 1997). Koshkarova (1995) also noted the gradual disappearance of the taiga species from the vegetation of modern shrub tundra after 450014C yr B.P. Temperatures might be about 1.5◦C and precipitation about 25 mm below modern values (Fig. 7).
Peat accumulation dramatically slowed or stopped in most sites during the Subboreal period. Processes of erosion and soil formation started on the top of many sequences. The surprisingly old ages from the upper part of LAO6, LAB2-95, LAO13, and LAB2-94 sites as well as an inversion of the radiocarbon dates from the top of LAB2-94 may reflect these processes. Such processes were common in many Arctic regions at this time (Peteet et al., 1998).
Only a few pollen spectra are available for the last millennia (LAB3-95, LAB2-95, LAO13, and LAB2-94), but they reflect the deterioration of environment in the area. Larix was gradually disappearing from the vegetation. The youngest14C age from larch macrofossils is 2880±6014C yr B.P. The only published pollen spectrum (a site west from the Labaz Lake) is14C dated to 3790±5014C yr B.P. (Nikol’skaya et al., 1980). The tundra taxa dominate in the spectrum, indicating modern-type vegetation.
Plant remains from a peat profile near the Lama Lake were14C dated to 2810±4014C yr B.P. and also demonstrate that modern vegetation and climate was established in that area at the end of the Subboreal period (Koshkarova, 1995). We assume that the vegetation in the Labaz Lake area became similar to modern at the end of the Subboreal period.
Climatic changes during the last several millennia are re- flected by only a few samples, with warm events reconstructed at about 3500, 2000, and 100014C yr ago. The cold event between 500 and 20014C yr ago (Little Ice Age?) is also reconstructed from these records (Fig. 7). Our TVIIreconstructions for the last 2000 14C yr are similar to TVII reconstructed from Larix tree rings from eastern Taymyr (Briffa, 1999).
CONCLUSIONS
Radiocarbon-dated records provide the first detailed vege- tation and climate reconstruction for the last 48,000 14C yr in the central part of Taymyr Peninsula (Table 3). Larix for- est with shrub Alnus and dwarf Betula grew near Labaz Lake
TABLE 3
Vegetation and Climate Reconstruction for the Last Radiocarbon 48,000 yr in the Labaz Lake Area
Period, age Dominant vegetation type Climate reconstruction
Late Holocene, ca. 250014C yr B.P.–today Vegetation became similar to southern tundra type
Coolings at 2500 and 500–25014C yr B.P.
Early–Middle Holocene, ca. 9400–290014C yr B.P. Open Larix forest with some tree Betula and Alnus fruticosa
Coolings about 9600, 8200, and 450014C yr B.P.; warming at 8500 14C yr B.P., the warmest interval ca. 8000–450014C yr B.P.
Late Glacial/Holocene transition, ca. 10,00014C yr B.P. Betula nana–Alnus fruticosa shrub tundra T up to 1.5◦C and P 50 mm higher than today Younger Dryas, ca. 10,50014C yr B.P. Increase of herb presence in vegetation T up to 3◦–4◦C and P 100 mm less than today Allerød, ca. 11,50014C yr B.P. Increase of shrub presence in vegetation T up to 1.5◦C and P 25 mm higher than today Sartan (Late Weichselian) Stade, ca. 24,000–10,30014C yr B.P. Steppe-like communities with Artemisia;
Poaceae and tundra communities with Betula nana, Dryas
T up to 4◦–5◦C and P 75–100 mm less than today during the coldest interval, ca.
18,000–20,00014C yr B.P.
Late Kargin Interstade, ca. 28,00014C yr B.P. or later Vegetation similar to modern Larix taiga near its northern limit
T about 1◦C and P about 50 mm higher than today
Late Kargin Interstade, ca. 28,600–28,80014C yr B.P. Betula nana dominated vegetation Climate similar to modern
Late Kargin Interstade, ca. 30,00014C yr B.P. Larix taiga with Alnus fruticosa T about 2◦C and P about 100 mm higher than today
Middle Kargin Interstade, ca. 33,000–30,00014C yr B.P. Open Larix forests with Betula nana and some Alnus fruticosa
Relative deterioration of climate Middle Kargin Interstade, 33,60014C yr B.P. or prior Larix forests with Alnus fruticosa and
Betula nana
T up to 1.5◦C and P 50–75 mm higher than today
Beginning of Middle Kargin Interstade, ca. 44,000–
42,00014C yr B.P.
Open Larix forests with Betula nana and some Alnus fruticosa
T up to 0.5◦C warmer and P 25 mm higher than today
Early Kargin (Middle Weichselian) Interstade,>48,00014C yr B.P. Larix forest with Alnus fruticosa and Betula nana
T up to 2.5◦–3◦C warmer and P 75–100 mm higher than today
T—temperature; P—precipitation.
during the Kargin (Middle Weichselian) Interstade, ca. 48,000–
25,00014C yr ago. The climate was generally warmer and wetter than today.
Open steppe-like communities with Artemisia, Poaceae, Asteraceae, Cyperaceae, and Caryophyllaceae as well as tundra- like communities with dwarf Betula, Arctic Salix, Dryas, Saxifraga, Oxyria, and Carex dominated during the Sartan (Late Weichselian) Stade, about 24,000–10,30014C yr B.P. The cold- est climate occurred between 20,000–17,000 14C yr B.P. At about 12,000 14C yr B.P (the Allerød Interstade?) TVII was 1.5◦C warmer than today. The climate deterioration at the late Sartan corresponds to the Younger Dryas. Temperature could be 3◦–4◦C and precipitation about 100 mm lower than modern values.
Sartan tundra-steppe vegetation was replaced by Betula nana–
Alnus fruticosa shrub tundra about 10,00014C yr B.P. Larix ap- peared in the area about 940014C yr B.P. and disappeared after 290014C yr B.P. Coolings at about 9600 and 820014C yr B.P.
characterize the first half of the Holocene. A warm event oc- curred about 850014C yr B.P., and the Holocene temperature maximum took place during the second half of the Atlantic pe- riod, from 6000 to 450014C yr B.P. The vegetation cover became similar to that of the present day at the end of the Subboreal pe- riod. Late Holocene warm periods occurred at about 3500, 2000, and 100014C yr B.P. A cooling (Little Ice Age?) took place ca.
250–20014C yr ago.
The climate reconstructions show that the warm periods are defined primarily as times of increased summer temperature rather than winter ones. Precipitation trends parallel the tem- perature shifts. During warm periods precipitation increased, whereas it decreased during the cold periods. The reconstructed climatic fluctuations are in good agreement with climate events reconstructed from other areas in northern Eurasia. For better resolution climate reconstructions new high-resolution pollen records from the Taymyr Peninsula are necessary.
ACKNOWLEDGMENTS
This research was made possible through the Helmholtz Association of Na- tional Research Centers project, “Natural Climate Variations from 10,000 Years to the Present Day.” We would like to thank Drs. P. M. Anderson, D. Yu.
Bol’shiyanov, N. Bigelow, and anonymous reviewers for their critical and helpful comments on the manuscript.
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